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Old Mar 1st 2019, 01:19 AM   #1
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Engineering optics

Hi everyone, Iím not sure about the solution of this question.
I know that chromatic aberration would occur and because if that the focal length of the lens would be affected.


Can anyone please help me solve this question. I have been caught up with this question for quite long. TIA
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Old Mar 1st 2019, 03:37 AM   #2
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Chromatic aberration occurs because the refractive index of the glass varies with wavelength (colour),
which causes different colours to be focused at (slightly) different focal lengths.
This is an inescapable consequence of the interactions between light and the materials it passes through.

As shown on your attached chart different materials have different refractive indices,
and the variability of the refractive index with respect to colour also varies with material.

So at first glance you want the flattest response with respect to colour,
however, this occurs in the lower refractive index materials.
A lower refractive index means you will need a thicker and more sharply curved lens to get the same focal length.

Chromatic aberration is also a function of the angle at which the light hits the surface of the lens,
A larger angle means a larger chromatic aberration,
thus a more sharply curved lens will mean more chromatic aberration.

Thus there needs to be a balance between the variation of the refractive index with colour, and the required thickness of the lens.
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